1. Technical Field
The present invention relates to an optical diffraction element having different diffraction efficiencies due to the polarization direction of incident light, an optical pickup using the optical diffraction element, and a method of manufacturing the optical diffraction element.
2. Related Art
An optical diffraction element has many uses, and is often used in an optical pickup that reads data from an optical storage medium such as a CD, DVD, or Blu-ray (Registered Trademark).
Patent Document 1 discloses a diffraction element. This diffraction element includes a substrate in which recessed portions are formed periodically in one surface via etching. In this diffraction element, the laser light is diffracted and separated by the regions in which the recessed portions are formed and the other regions.
Patent Document 1: Japanese Patent Application Publication No. 2008-21368
However, in the substrate of the diffraction element described above, the region where the recessed portions are formed is thin, and therefore the thickness is increased in order to maintain enough strength. Furthermore, in order to prevent light from returning to the laser, the diffraction element uses a polarization filter and a half-wave plate affixed thereto. As a result of affixing these components, the overall apparatus in which the diffraction element is included becomes larger, which is a problem.